Help with deciphering soft knocking sound

[challis0124]

I am not sure where this post belongs because I'm not sure exactly what the culprit is, so I'm hoping someone here can shed some light.

I am currently on an Island packet sailboat at anchor in an area with strong current and tide shift. I just noticed this evening there is a soft rhythmic knocking coming from somewhere on the boat...I can't pinpoint its location it sound like it's everywhere and nowhere. But it's continuous. Every few seconds it knocks 5 times then stops for a few seconds and starts up again.

I don't know if it's something on the deck( though I have checked all rigging and nothing that looks or sounds like this.) I live aboard my boat so am very attune to her sounds. I don't think it's anything on the engine, though I have heard prop shaft could cause something tho I'm not sure that's it either...maybe anchor chain ( though I doubt it). It almost reminds me of a woodpecker

Maybe a ghost

Any thoughts or if you have ever experienced this ? Much appreciated!

[exkma367]

The one that drove us nuts was the wires inside the mast. Next time we had the mast down we ran conduit.

[donradcliffe]

Is the strong current new?? Is your prop turning??

[challis0124]

This is our second night in this anchorage wit fairly strong current, but this isn't new for us as we've been in strong current for months. Checked prop in all positions w no change in sound. There are strong winds also and still remains constant. It's definitely a mystery

[challis0124]

Checked the mast but doesn't sound like it's in there. Can only hear it from inside the boat outside you can't hear it at all.

[gamayun]

Because it's such a consistent sound, I would check all your pumps and motors. Do you have a mechanical fuel pump? I accidentally switched on my diesel heater's fuel pump just before I went to bed a while back. It woke me up in a crazy panic in the middle of the night when the sound got really loud inside the engine compartment right next to my head. A tapping like you're hearing would drive me insane...

[a64pilot]

The rudder can knock if current is right.
What year and model, have you had the lower part of the rudder shimmed in the shoe?
Try turning the rudder to one way completely to see if it changes the noise, do you have the optional rudder lock? If so engage it with rudder turned.
I'd try turning off the battery switch unless your sure it can't be something like the water pump or something. Just to eliminate possibilities.
If conditions are right, the water can slosh in the tank.
Any chance it's the leak at the prop shaft, dripping water? Deep bilge.


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[JPA Cate]

Your description of the sound makes it seem to me that it is activated by the boat's motion at anchor. I'd check for anything stowed somewhere where it is rocking back and forth. My boat has cupboard doors that can make that kind of sound when we roll, but also tall small diameter bottles tend to bump back and forth.

The pause, bump, bump, bump, bump, bump and repeating doesn't sound right for internal halyards or for any of the kinds of pumps we have, but who knows? You are familiar with all your pump sounds? Lots of things sometimes bump the boat, but not that regularly. 'Tis a puzzlement.

Ann

[chris95040]

Oh man. That's gonna be a special kind of satisfaction when you figure this one out.

Be a pal and let us know what you find.

[gamayun]

OH! Is your computer on? Maybe the fan is going bad....

[Siberianhusky]

Spent a couple hours one night trying to find a knocking noise.
Somebody had moved a bilge pump handle, when the boat would rock the handle would roll and hit the hull. Sounded like it was comming from every direction. Drove me nuts!
Could be anything, start at one end and work you way to the other.
My search started on deck looking overboard around the waterline for something floating. Handle turned out to be behind the stove in the galley rolling back and forth on the counter completely out of sight....

[l2ridehd]

Also had this on an Island Packet and it took a while to find as it sounded like it was something in the aft cabin. Turns out it was the spare propane tank rocking against the inside of it's storage locker.

[Privilege]

I recon'....because your anchor is out you don't have the normal pile of chain in your chain locker. The remaining chain running from the deck to the bottom of the anchor locker is swinging rhythmically and tapping on what's left of the chain pile or the locker wall.

[Hud3]

I was anchored in a strong current once, and it turned the boat around so that the small, wind-generated waves slapped the stern under the overhang. It made a soft knocking noise.

[Reach]

Originally Posted by Ann T. Cate

Your description of the sound makes it seem to me that it is activated by the boat's motion at anchor. I'd check for anything stowed somewhere where it is rocking back and forth. My boat has cupboard doors that can make that kind of sound when we roll, but also tall small diameter bottles tend to bump back and forth.

Ann

Originally Posted by l2ridehd

Also had this on an Island Packet and it took a while to find as it sounded like it was something in the aft cabin. Turns out it was the spare propane tank rocking against the inside of it's storage locker.

From your description I'd lean towards these ideas above. It sounds like something round with a short roll/bump frequency at anchor. I've heard similar soft thumps with a mag flashlight rolling for example.

Good luck finding the culprit!